This invention relates to compositions of matter useful as lubricants and hydraulic fluids and more particularly to silicon-hydrocarbon compositions of matter which may be used as lubricants and in various hydraulic systems where extremes of temperatures are encountered.
Hydraulic fluids having good viscosity-temperature viscosity-volatility and stability characteristics are very desirable. For instance, hydraulic fluids should in the broadest sense have viscosities high enough to satisfy the hydrodynamic requirements of the hydraulic pump and other elements of the hydraulic loop at the upper temperature extreme experienced and yet be low enough to flow freely at the lowest temperature expected. Attempts to attain such hydraulic fluids by the use of organosilicone materials have in general not proven particularly satisfactory. By way of illustration, silicone oils [i.e. materials having the formula Me.sub.3 SiO(Me.sub.2 SiO).sub.x SiMe.sub.3 ] are not readily compatible with the elastomers ordinarily used in hydraulic systems. For instance, they tend to shrink SBR rubber gaskets often present in hydraulic systems which results in leakage of the silicone oil from the system. Silicone oils also have relatively poor lubricity for the metals conventionally used in hydraulic systems and hence relatively high wear is encountered when silicone oils are employed in such systems. Attempts to solve the disadvantages of such silicone oils by the addition thereto of conventional petroleum and other organic hydraulic fluids and/or the addition of conventional inhibitors such as anti-oxidants, rust and corrosion inhibitors, anti-wear agents, dispersants, and the like, have in general also not proven particularly successful since such silicone oils have exhibited very little ability if any to dissolve said conventional materials.
More recently liquid alkoxysiloxanes as disclosed in U.S. Application Ser. No. 579,600 filed May 21, 1975 have been proposed for use as a hydraulic fluid, as have mixtures of such types of alkoxysiloxanes along with a glycol ether phosphoric acid ester in U.S. Application Ser. No. 626,703 filed Oct. 29, 1975, now U.S. Pat. No. 3,974,080. In addition, hydraulic fluid compositions of an alkoxysiloxane and a hydrocarbon oil component selected from the group of naphthenic oils, branched chain aliphatic hydrocarbon oils and alkylated aromatic oils are disclosed in U.S. Application Ser. No. 656,387 filed Feb. 9, 1976, while compositions comprising a dimethylsiloxane oil and a hydrocarbon oil component selected from the group of naphthenic oils, branched chain aliphatic hydrocarbon oils and alkylated aromatic oils for use as lubricants and hydraulic fluids are disclosed in U.S. Application Ser. No. 656,386 filed Feb. 9, 1976, now U.S. Pat. No. 4,097,393. However, none of the above applications disclose the compositions of the instant invention.
It has now been discovered that silicone-hydrocarbon compositions of matter can be prepared which are useful as lubricants and hydraulic fluids and which have excellent viscosity-temperature, viscosity-volatility and thermal stability characteristics.